Question: Emily is 40 years old and Luis is 8 years old. How many years will it take until Emily is only 3 times as old as Luis?
Solution: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Emily will be $40 + y$ years old and Luis will be $8 + y$ years old. At that time, Emily will be 3 times as old as Luis. Writing this information as an equation, we get: $40 + y = 3 (8 + y)$ Simplifying the right side of this equation, we get: $40 + y = 24 + 3 y$ Solving for $y$ , we get: $2 y = 16$ $y = 8$.